1. Field of the Invention
This invention relates to methods for inhibiting tumor cell proliferation. More particularly this invention relates to a method for inhibiting tumor cell proliferation by enhancing the patient's ability to respond immunologically to the tumor.
2. Description of Related Art
Traditional therapies have done little to alter the outcome for patients with high-grade brain tumors, such as glioblastomas, and many other types of tumors, such as systemic melanoma, and cancers of the head and neck. Patients with resectable primary tumors generally experience recurrence of the tumor within one year after surgery, chemotherapy, or radiation. Often these tumors progress rapidly, with or without further conventional therapy. Thus, there is the need to develop new modes of therapy for these deadly tumors.
A new family of cancer therapies developed. in recent years are based on immunotherapy. In general, tumor immunotherapies take one of two approaches: 1) various techniques are employed to activate the patient's immune system to attack the tumor; or 2) the lymphoid cells of the patient are removed and activated by in vitro techniques to produce anti-cancer activity, and the activated cells are then systemically reintroduced into the patient. The clinical effectiveness of these various types of immunotherapy are being evaluated in patients with different types of cancers. However, one of the major problems associated with both of these types of immunotherapy is toxicity observed when immunotherapeutic agents are administered systemically. A method developed to avoid this toxicity is intralesional administration of immunotherapy, for instance by injection directly into the tumor. Intralesional administration of various forms of immunotherapy to cancer patients does not cause the toxicity seen with systemic administration of immunologic agents (M. Fletcher, et al., Lymphokine Res. 6:45, 1987; H. Rabinowich, et al., Cancer Res. 47:173, 1987; S. A. Rosenberg, et al., Science 233:1318, 1989; and G. Pizz, et al., Int. J. Cancer 34:359, 1984).
Recent studies indicated that immunization of animals with tumor cells that were genetically engineered to secrete different cytokines enhanced the induction of a therapeutic immune response. The cytokines are believed to induce a complex set of reactions including: a) increased expression of tumor antigens; b) inflammation and infiltration of the tumor with host lymphoid cells; c) induction of tumor specific immunity; and d) activation of both nonspecific and specific host anti-tumor effector mechanisms, which destroy the tumor. However, although this technique may ultimately prove useful, because it is extremely costly and time consuming, its application may be limited.
Studies in experimental animals (primarily mice) show that the chronic release of cytokines within a tumor may induce a host anti-tumor response and tumor regression. Repeated intralesional injection of cytokines such as Interleukin-2 (IL-2), Tumor Necrosis Factor (TNF) and Interferon-.gamma. (INF-.gamma.) has been shown to cause regression of cutaneous sarcomas (S. P. Creekmore, et al., Resident and Staff Physician 34:23-31, 1988; P. Greenberg, et al., Basic and Tumor Immunology (R. Herberman, ed.) p. 302, 1983; E. Grimm et al., Lymphokines, 9:279-311, 1984; G. Forni, et al., Lymphokines 14:335-360, 1987). It has also been shown that injection into a tumor of the animal's tumor cells that have been genetically engineered to secrete cytokines such as IL-2, IL-4, TNF and Granulocyte Monocyte Colony Stimulating Factor (GM-CSF) will induce host anti-tumor immunity (E. Feron, et al., Cell 60, 397-403, 1990; P. Galumbek, et al., Science 254:713-716, 1991; A. Ascher, et al., J. of Immunol. 146:3227-3234, 1991). These latter results have been obtained even in treatment of tumors that were previously thought to be non-immunogenic.
J. M. Redd, et al. (Cancer Immunology and Immunotherapy 34(5):349, 1992) have shown in rats that allogeneic lymphocytes sensitized against donor alloantigens can inhibit tumor formation when co-injected into the brain of a rat with 9L glioblastoma. In a separate study, both normal and alloimmune spleen cells from Wistar rats were injected into established 6-day T9 brain tumors in the Fischer rat. Intralesional injection of normal Wistar spleen cells from Wistar rats, previously immunized against Fischer alloantigens, cured the tumors in 50% of the Fischer rats. In contrast, untreated animals and non-responders died within 30 days. Survivors appeared completely normal and intracranial injections of allogeneic cells into normal rats caused no detectable change in behavior or survival over a three month period. Histopathologic examination of brains from treated tumor bearing animals revealed: a) mononuclear cell infiltration, massive tumor necrosis beginning at 2 to 4 days and total tumor destruction by 15 days; or 2) cellular infiltration, early tumor destruction and then tumor regrowth progressing to death of the animal. No damage to normal brain tissue was evident at any time in these animals. Tumor regressor animals developed systemic immunity, for they proved totally resistant to intracranial rechallenge with viable tumor. Although these results in rats are of interest, their value in reasonably predicting what would be seen in a highly unrelated species, such as a human, is highly questionable in view of the considerable species diversity which exists, especially with respect to the immunological response to tumors.
Human glioma patients with localized and surgically accessible tumors are logical candidates for intralesional immunotherapy. Multiple Phase I studies in adult patients with gliomas have been reported employing intratumor implants of autologous peripheral blood lymphocytes activated in vitro with IL-2. While little clinical effect was noted, negative side effects were few and occurred only when excessive levels of IL-2 were co-administered with the cells (K. S. Jacobs, et al., Cancer Res., 47:2101, 1986; R. Merchant, et al., Neurosurgery 23:725, 1988). Studies of these patients revealed that survival correlated directly with the ability of implanted cells to secrete the cytokine TNF. The discovery of inhibitors for both TNF and IL-1 in the serum or tumor cyst fluid, and in primary cultures of the tumors from these patients suggests the tumor cells surround themselves with agents that block the host anti-tumor response. These inhibitors may prevent cytokine activated implanted cells from remaining active in the tumor long enough to cause its destruction. This concept is supported by findings in brain tumor studies in rats. When IL-2 active lymphoid cells were implanted into C6 and T9 glioma brain tumors in Wistar and Fischer rats, respectively, histopathologic examination revealed the implanted IL-2 activated lymphoid cells only remained in the tumor site for 4 to 6 days (W. Carson et al., J. of Immunotherapy 10(2):131-140, 1991).
The mechanisms operative in causing tumor regression in the animals treated with allogeneic lymphoid cells include a graft vs. host and host vs. graft reaction in the tumor site. These powerful immunologic reactions may stimulate high levels of endogenous cytokine production in the tumor, overcome local levels of cytokine inhibitors, and presumably stimulate infiltration, recruitment and activation of both specific and non-specific host anti-tumor activity. The tumor regressor animals were found to be resistant to tumor rechallenge. However, it has heretofore been unknown whether any treatments based on similar methods would achieve similar results in human subjects sufficient to be considered effective in the treatment of human tumors.
Therefore, in view of the limitations of the prior art, new and better methods for treating mammalian tumors are needed. In particular, new methods of intratumor immunotherapy are needed for human cancer patients for whom regression of an individual solid tumor could prove life saving.